1. Field of the Invention
This invention relates to a recording apparatus for recording using a recording head and more particularly to a recording apparatus having a stand-by mode which interrupts and resumes recording during recording.
2. Related Background Art
As this type of recording apparatus, digital recording devices such as an ink jet recording type and a thermal transfer recording type have been well known so far.
Especially, an ink jet recording apparatus has merits such as easy coloring, and prevails as, for example, an output device, etc. for computer graphics.
FIG. 7 is a block diagram showing the constitution when the ink jet recording apparatus is used as an output device for computer graphics. In FIG. 7, numeral 101 is a host computer, numerals 102 and 104 are image signals, numeral 103 is an interface, and numeral 105 is an ink jet printer. Image data, which the host computer 101 has therein, is transmitted to the interface 103 as an image signal 102, and is once stored in a memory (not shown) in the interface 103.
The interface 103 converts the image data within the memory into such a form that can be processed by an ink jet printer, and then transfers it to the ink jet printer 105 as an image signal 104. The ink jet printer 105 records in accordance with the transferred image signal 104.
In the above constitution, the capacity of the memory, in the interface 103, is generally several megabytes to several tens of megabytes, but the amount of image data which the host computer 101 has may exceed this capacity sometimes. In such a case, the host computer 101 is capable of transferring data only for the capacity of the memory in the interface 103 and after finishing recording based on these data, further transferring the remaining data for recording based thereon.
At this time, the printer 105 records on the basis of the data from the interface 103, and interrupts carrying of the recording sheet and driving of the recording head to stand by until the next data is transferred. This enables the system with the above-mentioned constitution for recording an image to cope with a larger amount of image data than the memory capacity of the interface 103 for recording on the basis thereof.
The recording apparatus having a stand-by mode for interrupting such a recording operation had the following problem. That is, the density of an image to be recorded may be discontinuously different before and after the stand-by. This is undesirable from the stability point of view in recording, and the image quality will be noticeably impaired especially when the above-mentioned change in density occurs on the same recording sheet.
FIG. 8 is a diagram of a typical recording sheet when the above-mentioned stand-by state occurs while a sheet of recording sheet is being recorded. In FIG. 8, it is assumed that the recording width of a recording head, that is, the length of the range in which discharging orifices are arranged, is d in the ink jet type recording head, and the recording head records images by scanning in the X direction in FIG. 8. Although an image for 14 scans in total can be recorded on a sheet of the recording sheet shown in FIG. 8, the memory capacity of the interface 103 is assumed to have only five scans.
In such a case, recording is first continuously performed on a portion shown by A in FIG. 8, and thereafter the recording head enters a stand-by state until image data for a portion shown by B is transferred. After this transfer is finished, recording is continuously performed on the B portion, and thereafter the recording head enters the stand-by state again until the image data for a C portion is transferred. After this transfer is finished, recording is continuously performed on the C portion to finish recording on a sheet of recording sheet.
When the recording head continuously records, its temperature generally rises. For example, in the ink jet type recording head, a discharge energy generating element to discharge ink generates heat energy with discharging to raise the head temperature. Also in the thermal transfer type recording head, the heat generated by the heating element raises the head temperature. When the temperature thus rises, the ink viscosity lowers and the ink discharge increases to increase the recording density, for example, in the ink jet type recording head. Also in the thermal transfer type, the amount of ink to be transferred onto the surface increases to increase the density in the same manner.
However, once the recording head enters a stand-by state for recording, the temperature lowers, and the recording density may lower in recording immediately thereafter. This phenomenon is seen with different types of recording heads, and is noticeable especially in the ink jet type recording head in which a heater is caused to generate heat to boil ink and ink is discharged by the pressure of bubbles generated thereby.
Changes in the recording density when such an image as shown in FIG. 8 is recorded are shown in FIG. 9.
Since when recording is continuously performed as shown in FIG. 9, the temperature of the recording head rises little by little and the density increases as the temperature rises, the change in density is not noticeable. When, however, the recording stand-by state shown by points of time D and E in FIG. 9 intervenes, a change in density abruptly occurs with lowered temperature of the recording head. As a result, a problem occurs in the image to be recorded that the difference in density between portions recorded before and after such a stand-by state is very noticeable.
To reduce the above-mentioned change in density by keeping the head temperature before and after such a stand-by state within a fixed range, a method has been well known so far in which the recording head is provided with temperature detecting means such as a thermistor and a heat insulating heater and the heat insulating heater is driven in accordance with the heat temperature detected by the temperature detecting means to control the temperature. In addition to this, another method was also well known in which a fan is provided and is driven if the head temperature is higher than the preset temperature.
However, this type of temperature control is slow in response while the temperature is abruptly changing, and it is difficult to precisely control the temperature when the temperature comparatively abruptly changes as shown by the points of time D and E in FIG. 9. Especially when one recording head is provided with one each of thermistor and heater to control the entire recording head to a fixed temperature, the ink temperature in the liquid channel, where the discharge energy generating element is disposed and the discharge energy is applied to ink, does not reach the predetermined temperature even if a temperature to be detected by the thermistor reaches a predetermined temperature. Recording in this state frequently leaves a difference in density. For this reason, in order to overcome this phenomenon, it is regarded as necessary to heat the ink in the liquid channel, which directly relates to discharging, to the predetermined temperature as fast as possible.
In the above-mentioned conventional image recording apparatus, however, when the recording head continuously prints, the head temperature mostly exceeds the predetermined temperature even if the fan is driven. When the head interrupts the recording and enters the stand-by state in this state, such a change in density as mentioned above still occurs because the recording head temperature continues lowering until the predetermined temperature is reached.